Because of their clarity and altitude, exposure to ultraviolet radiation in mountain lakes can be extremely high. This study was conducted in four montane lakes in Jasper National Park. Its focus was twofold: first, to examine the direct effect of ultraviolet radiation on both benthic invertebrates and epilithon, the rock-dwelling matrix of algae, bacteria, and detritus. Second, to examine the indirect effect of ultraviolet-mediated shifts in epilithic composition on invertebrates. Although ultraviolet radiation decreased epilithic carbon accrual and pigment concentrations, total algal biomass was not affected. Furthermore, although exposure to ultraviolet radiation decreased invertebrate colonization, it increased food quality for invertebrates, through decreased carbon to nutrient ratios and increased fatty acid concentrations. These effects, however, were weak, and not universal across our four study lakes. Our results suggest that although ultraviolet radiation can play an important role in structuring freshwater benthic communities, other factors, such as nutrient availability, may often be of paramount importance.